1. Field of the Invention
The subject invention is directed to mechanisms for accessing the reservoir of implantable medication infusion devices and, more particularly, to resealing septums used in such devices.
2. Description of the Prior Art
Implantable medication infusion devices designed to infuse medication into a patient's body at a controlled dosage and rate have been known in the prior art. These devices have included reservoirs for storing a supply of medication that will permit continued operation of the device for a specified period before the supply must be replenished.
Most prior art infusion devices have included some mechanism to access the reservoir for refilling purposes. Many of those devices have provided a septum for this purpose. The septum was a membrane that could be penetrated by a needle but that would reseal when the needle was withdrawn. Examples of infusion devices incorporating such septums are shown in U.S. Pat. Nos. 3,951,147; 4,221,219; 4,229,220; and 4,360,019 as well as U.S. patent application Ser. No. 439,138 filed Nov. 11, 1982 by Robert E. Fischell
One disadvantage of devices employing refill septums as disclosed in the prior art was that, after the septum had been penetrated a number of times, it had a potential for leakage at the point of penetration. Since the infusion devices were intended for human implantation, correction of such a leakage problem would necessitate subjecting the patient to a surgical procedure. Thus, there was a need in the prior art for an improved septum having extended resealing capability.
To reduce the potential for leakage from the infusion device through a septum leak or through various other failure modes, some more recent infusion devices have incorporated reservoirs that are maintained at less than atmospheric pressure. In these devices, leaks would tend to cause body fluids to leak into the reservoir as opposed to permitting medication to escape.
In these below-atmospheric pressure systems, a valve was provided between the septum and the reservoir to isolate the septum from the reservoir and help maintain the lower absolute pressure therein. In one particularly advantageous arrangement, a cavity was provided adjacent the septum with a poppet valve located therein. In the closed position, the poppet valve isolated the septum from the reservoir. The poppet valve could be mechanically opened by a needle inserted through the septum. This was advantageous in that the reservoir could be refilled passively by inserting the needle through the septum to open the poppet valve and then venting the supply of medication to atmospheric pressure. The pressure differential thus established would cause the medication to flow into the reservoir. If the needle was improperly positioned, the poppet valve would not be opened so that there would be no pressure differential to establish flow of the medication out of the vial. This insured that the needle was properly placed through the septum in communication with the reservoir and avoided the possibility that the medication would inadvertently be injected directly into the body. An example of this type of system is shown in U.S. patent application Ser. No. 327,818 filed Dec. 7, 1981 by Robert E. Fischell.
The cavity and poppet valve arrangement for infusion devices having below-atmospheric pressure reservoirs required that the poppet valve engage the septum to form a tight seal therebetween. However, prior art designs for the spetum did not produce a reliable seal between the poppet and the septum. Thus, in addition to a septum having improved resealing capability, there was also a need for an improved seal formed by the poppet.